1. Field of the Invention
This invention relates generally to the separation of oxides of heavy isotopes of hydrogen, and in particular to a process and apparatus for separating deuterium oxide (HDO, D2O), tritium oxide (HTO, D2O) and oxides of deuterium and tritium (DTO) from light water (H2O) contaminated with heavy isotopes of water. In addition, this process addresses separation of heavy water isotopes, e.g. DTO from D20, and HTO from D20.
2. Description of Related Art
Nuclear power plants must routinely deal with the replacement and disposal of contaminated water taken from the core reactor that is laden with heavy isotopes of hydrogen, namely deuterium oxides, tritium oxides and deuterium-tritium oxides. Tritium in particular is highly radioactive having a half-life of about twelve and one half years emitting beta rays to form helium.
Periodically, the contaminated water from nuclear reactors must be replaced. It has become industry practice of dispose of the old contaminated water by simply dispersing it over adjacent ground areas or evaporating the contaminated water into the atmosphere. This is stressful to the environment as the deuterium oxides and tritium oxides are now known to have contaminated ground water sources. One alternative is to sequester contaminated water in concrete at a considerable expense.
In accordance with the teaching in U.S. Pat. No. 6,348,153 by Patterson, et al., a process and related apparatus are described for separating deuterium oxide (HDO, D20) and tritium oxide (HTO, T20), i.e. heavy water and tritiated water, and deuterium-tritium oxides, from wastewater. As used herein, water molecules of the formula H20 will be referred to as light water molecules, or simply water molecules, while water molecules in which one or both of the hydrogen atoms have been replaced by one of these hydrogen isotopes will be referred to as isotope water molecules or isotope molecules.
In the described prior art process, a portion of the isotope water molecules are removed from contaminated water, i.e., water containing a small amount of isotope water molecules, through selective adsorption by contacting the contaminated water with a molecular separation material containing hydration sites carrying one or more associated waters of hydration. In the process, isotope water molecules present in the contaminated water selectively replace a portion of the waters of hydration associated with the hydration sites. The molecular separation material can then be separated from the water, reducing the percentage of isotope molecules in the water. After separation, the molecular separation material can be regenerated by removing the isotope molecules for long-term storage, and reused repeatedly to separate isotope molecules.
In order to improve the efficiency of the selective adsorption process, the percentage of isotope molecules in the contaminated water can be increased, thereby increasing the exposure of isotope molecules to hydration sites, by removing a portion of the light water molecules, before or during the selective adsorption, by bringing the contaminated water into contact with a porous film or membrane that exhibits a greater permeability for light water molecules than for the larger isotope molecules. For some purposes, adequate separation may be effected through membrane separation alone.